Compounds consisting of polyolefin and a partially crosslinked rubber phase possess good properties as thermoplastic elastomers (TPEs) such as heat resistance, mechanical strength, flexibility and elasticity etc., but their flowability is poorer than generally used thermoplastics, leading to problems such as flow marks in the manufacture of large molded parts. In order to resolve these problems, for example, partially crosslinked compounds of polyolefin and two rubber components (Japanese Pat. No. 54-23702), partially crosslinked compounds in which polyolefin is blended with a composition of a polyolefin and a rubber component which was treated in the presence of organic peroxide (Japanese Pat. No. 56-15743) as well a the method of manufacture of such compounds (No. 56-15740) have been proposed.
These inventors have developed compounds in which a polyolefin is added to a composition consisting of halobutyl-containing rubber phase which is partially crosslinked with a polyolefin, using metal oxide (MOx) and/or metal chlorides (MCl) as vulcanizing agents. In addition, the method of manufacture of TPE compositions including styrenic rubber has been proposed, for example Japanese Patent Appl. No. 59-6236 proposes manufacture of compositions containing a hydrogenated styrene-conjugated diene block copolymer, softening agents, olefinic resins, peroxide-curable olefinic rubber, an uncrosslinked hydrocarbon rubber and inorganic fillers, in which the peroxide-curable rubber is partially crosslinked.
Although the above-mentioned compositions possess good properties as thermoplastic elastomers (TPEs), in comparison to polyurethane (PU) type elastomers they suffer from inadequate high temperature physical properties and inadequate gloss for a high quality appearance. The present invention prevents the decrease in stiffness with increased temperature and improves the gloss of molded parts for a high quality appearance, without loss in the properties of olefinic TPEs.